The present innovation finds application in magnetic resonance imaging (MRI) systems, particularly with regard to fat suppressed MRI and fat quantification with MRI. However, it will be appreciated that the described techniques may also find application in other imaging systems, other magnetic resonance scenarios, other image data collection techniques, and the like.
When measuring an “echo,” a B1 field is generated parallel to a longitudinal axis through an examination region of an MR scanner, which causes cellular nuclei in the examination region to momentarily align with the B1 field. Different materials (e.g., fat and water) nuclei resonate or “spin” back to their original positions at different rotational velocities. An echo is caused and detected by the MR scanner, such as by reversing the B1 field. The nuclei of different materials are at different positions in their respective rotations at the time the echo is generated (e.g., “echo time”) due to their different rotational velocities, and can thus be differentiated during image reconstruction. Other techniques employ for instance gradient-echo instead of the described spin-echo acquisitions.
The suppression of lipid signal is a common requirement in numerous applications of MRI. Moreover, a simultaneous quantification of water and fat signal receives growing interest lately, for instance in the context of obesity and metabolic disorder diseases. One approach to meet both demands is Dixon imaging, which is based on the different chemical shift of water and lipid protons and resulting phase differences between the signals from them at different echo times, which permit a retrospective separation in image reconstruction.
In particular in rapid imaging, Dixon imaging is typically performed with two different echo times only to keep scan times as short as possible. Available two-point Dixon methods impose constraints on the water-fat angle at the different echo times used for data acquisition. These lead to reduced flexibility in sequence design and thus often to increased scan times.
For instance, one or both echo times have a fixed phase, which leads to increased scan times. That is, conventional Dixon imaging techniques employ at most only one variable or arbitrary phase echo time, while require at least one fixed phase echo time.
The present application provides new and improved systems and methods for distinguishing between materials (e.g., fat and water) having different resonant characteristics using an enhanced Dixon technique for MRI, which overcome the above-referenced problems and others.